In recent years, the contactless power transmission is attracting attentions with which the power is transmitted in a contactless manner from the power transmitting side to the power receiving side. For example, the contactless charging device is increasingly developed which uses the technique of contactlessly transmitting power in order to charge the battery mounted in an electric vehicle. In such a contactless charging device, a spiral coil formed in a plane is mostly used as the coil for transmitting power or receiving power. However, as the coil for transmitting power or receiving power, in order to obtain sufficient properties, there is a problem that the size of coil becomes large.
As a means to solve such a problem, Patent Document 1 has disclosed a coil with a double layered structure which is obtained by connecting a spiral coil formed in the first layer and a spiral coil formed in the second layer in series. The spiral coil is usually used by disposing a magnetic plate made from a magnetic material and a metallic plate (such as an aluminum plate and a copper plate) made from a nonmagnetic metallic material on the back side of the coil, and thus a parasitic capacitance is generated between the conductor of the coil and the metallic plate. In addition, in the coil with a double layered structure, the distance between the conductor of the spiral coil formed in the first layer and the metallic plate is different from that between the conductor of the spiral coil formed in the second layer and the metallic plate, and thus the parasitic capacitance generated between the conductor of the spiral coil formed in the first layer and the metallic plate will differ from that generated between the conductor of the spiral coil formed in the second layer and the metallic plate.